Expert: Mark Janus - 6/5/2007

Question
Hi, Mark.  I work for a children's museum.  I am developing an exhibit on flying machines (both aircraft and spacecraft).  After two days of study, I'm trying to boil-down the what I have learned.  I've come up with this:
"A machine can fly if it has at least one of the following qualities:
1. it is lighter than air,
2. it has a shape that creates enough lift to overcome gravity,
3. it has sufficient vertical thrust to overcome gravity and drag,
4. or it is outside of earth’s atmosphere."
Yes, it's very simple- and I wish it could be simpler.  What I need from you- is it true?  Have I added or missed anything?  Thanks so much!


Answer
1. true
2. it has a shape that deflects air downward to create enough lift to overcome the forces of gravity
3. true
4  or it's outside the Earth's atmosphere with sufficient circumferential velocity as to balance the centrifugal force with the force of gravity


Sounds good to me....
mj